The need for increasing amounts of inexpensive reliable digital storage media continues to expand. Digital versatile disc (DVD) formats provide significantly more storage capacity than compact discs (CD) thus allowing more recording time with high density. To achieve the high density storage in a disc that has the same dimensions as a CD, the DVD disc construction includes two halves that are bonded together. Depending on the type of disc, the construction can vary, but typically includes two substrates each with metallic coatings.
The metallic coatings employed in DVDs may degrade over time with environmental exposure to heat, repeated temperature changes, oxygen, moisture, and other contaminants. Adding additional protective layers or changing base materials to overcome these problems can complicate manufacturing with additional equipment, expensive materials, and more process steps leading to decreased yields and increased costs.
It has been found that certain resins used in the DVD substrate bonding process may provide unsatisfactory environmental stability. For example, resins formed with constituents as outlined in Table 1 (values are amount in weight-percent of the total resin) and used to bond together two DVD substrates, one substrate with a pure silver coating and the other substrate with an aluminum coating, allow unit disc failure when subjected to a 21-day light exposure test, as detailed below. The metallic layers of test DVDs made with such resins turn black or darken to an unusable state prior to the completion of 21 days exposure, an unacceptable result. Consequently, the need exists for materials and processes that ease manufacturing, reduce costs, and increase disc life and reliability.
TABLE 1MaterialTypeExample 8Example 9Example 10Example 11BPE4EODA (bisphenol A 4 moleMonomer19.019.019.024.0ethoxylateddiacrylate)DPGDA (dipropyleneglycoldiacrylate)Monomer28.528.528.510.0TMPEOTAMonomer4.74.74.74.275(ethoxylatedtrimethylolpropanetriacrylate)2-PEA (2-Phenoxy Ethyl Acrylate)Monomer———15.0THF (tetrahydrofurfuryl acrylate)Monomer0.50.50.50.5Acrylated Expoxidized Soya Bean OilOligomer43.27543.27543.275—Aliphatic Urethane DiacrylateOligomer———40.0TPO (2,4,6-trimethylbenzoul-Photoinitiator———2.0diphenylphosphine oxide)CPK (1-Hydroxy-Cyclohexylphenyl-Ketone)Photoinitiator3.8——4.0BDK (Benzil Dimethyl Ketal)Photoinitiator—3.8——Darocure ® 1173 (2-hydroxy-2-Methyl-1-Photoinitiator——3.8—Pheny-1-Propane-leone)MEHQ (4-methoxyphenol)UV Stabilizer0.10.10.10.1Disparlon ® L-1985-50 (Kusomoto ChemicalsDe-gassing additive0.0250.0250.0250.025LTD)Genorad ® 40 (Rahn USA)Adhesion Promoter.1.1.1.1Total100.0100.0100.0100.021 Day Light Test*FailFailFailFail*Passing is less than 20% change in reflectivity after 21-day light test